Once upon a time, there were lots of picture books for children but not many stories for young-adult readers. Then along came Judy Blume. In the 1970s, the author of “Are You There God? It’s Me, Margaret,” spun pitch-perfect prose for adolescents and middle-schoolers, detonating a genre that exploded with wizards, babysitters, vampires and the junior-high drama of BFFs and frenemies.

The author, who will turn 80 in February, said, “50 years of writing…could be enough.” She is selling her literary archive to Yale University’s Beinecke Rare Book & Manuscript Library later this month.

Ms. Blume has published dozens of books, ranging from humorous children’s tales (a second-grader’s quixotic quest in “Freckle Juice”) to grown-up novels (enduring friendship in “Summer Sisters”). But she made her name with stories that resonated with pre-teens. She also took on subjects, including divorce and sexuality, that at the time were taboo for young readers. Ms. Blume’s candor drew fire from some quarters but earned her a world-wide following.

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The Beinecke, home to the papers of Gertrude Stein, James Joyce and others, also has a rich collection of children’s literature. Timothy Young, curator of modern books and manuscripts at the library, said the acquisition will turbocharge its growing young-adult holdings.

For some readers, Ms. Blume defines the genre. “If you ask anybody on the street to name a young-adult writer,” Mr. Young said, the response often is Judy Blume: “She is the iconic person that you’ve read and you loved or you didn’t love but you knew her work.”

Young-adult literature is a largely unexamined area of archival study, Mr. Young said, and one likely to attract faculty, researchers and visitors to Yale.

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Ms. Blume said she is no pack rat—in part because she moved houses often—but from the start she held on to the rejection letters that met many of her early efforts for very young children. She also kept the mockups of books that she submitted to publishers in her twenties. For those early attempts, she wrote rhyming verses, illustrated them with colored pencils and used brass fasteners to hold the manuscript together. Her creations “would come back rejected and every now and then I’d get a really nice rejection letter,” she recalled.

Ms. Blume also saved boxes of fan mail in which some readers revealed their hopes and fears. One 10-year-old wrote in ballpoint pen on a sheet of Garfield the Cat stationery “in every one of your books you give us a new way to cope with life.” Ms. Blume and Mr. Young said they are working with Yale’s legal advisers to allow access to the letters while preserving the young writers’ privacy.

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Ms. Blume said the $500,000 Yale is paying for the archive will go to the Kids Fund, her foundation through which she makes charitable contributions.